Permanent magnet materials are one of the important electric and electronic materials in wide ranges from various electric appliances for domestic use to peripheral terminal devices for large-scaled computers. In view of recent needs for miniaturization and high efficiency of electric and electronic equipment, there has been an increasing demand for upgrading of permanent magnet materials.
Major permanent magnet materials currently in use are alnico, hard ferrite and rare earth-cobalt magnets. Recent advances in electronics have demanded particularly small-sized and light-weight permanent magnet materials of high performance. To this end, the rare earth-cobalt magnets having high residual magnetic flux densities and high coercive forces are being predominantly used.
However, the rare earth-cobalt magnets are very expensive magnet materials, since they contain costly rare earth such as Sm and costly cobalt in larger amounts of up to 50 to 60% by weight. This poses a grave obstacle to the replacement of alnico and ferrite for such magnets.
In an effort to obtain such permanent magnets, RFe base compounds were proposed, wherein R is at least one of rare earth metals. A. E. Clark discovered that sputtered amorphous TbFe had an energy product of 29.5 MGOe at 4.2 K., and showed a coercive force Hc=3.4 kOe and a maximum energy product (BH)max=7 MGOe at room temperature upon heat treating at 300-500 degrees C. Reportedly, similar studies of SmFe.sub.2 indicated that 9.2 MGOe was reached at 77 K.
In addition, N. C. Koon et al discovered that, with melt-quenched ribbons of (Fe.sub.0.82 B.sub.0.18).sub.0.9 Tb.sub.0.05 La.sub.0.05, Hc of 9 kOe or more was reached upon annealing at about 875 K. However, the (BH)max of the obtained ribbons were then low because of the unsatisfactory loop rectangularity of the demagnetization curves thereof (N. C. Koon et al, Appl. Phys. Lett. 39(10), 1981, pp. 840-842, IEEE Transaction on Magnetics, Vol. MAG-18, No. 6, 1982, pp. 1448-1450).
Moreover, J. J. Croat and L. Kabacoff et al have reported that the ribbons of PrFe and NdFe compositions prepared by the melt-quenching technique showed a coercive force of nearly 8 kOe at room temperature (L. Kabacoff et al, J. Appl. Phys. 53(3)1981, pp. 2255-2257; J. J. Croat IEEE Vol. 118, No. 6, pp. 1442-1447).
These melt-quenched ribbons or sputtered thin films are not practical permanent magnets (bodies) that can be used as such, and it would be impossible to obtain therefrom practical permanent magnets. In other words, it is impossible to obtain bulk permanent magnets of any desired shape and size from the conventional melt-quenched ribbons based on FeBR and sputtered thin films based on RFe. Due to the unsatisfactory loop rectangularity or squareness of the magnetization curves, the FeBR base ribbons heretofore reported are not taken as practical permanent magnets comparable with the ordinarily used magnets. Since both the sputtered thin films and the melt-quenched ribbons are magnetically isotropic by nature, it is indeed almost impossible to obtain therefrom any magnetically anisotropic permanent magnets of high performance (hereinafter called the anisotropic permanent magnets) for practical purposes.
As mentioned above, many researchers have proposed various processes to prepare permanent magnets from alloys based on rare earth elements and iron, but none have given satisfactory permanent magnets for practical purposes.